The present invention relates to a storage system.
In general, a storage system includes one or more storage devices. Each of one or more storage devices generally includes, for example, an HDD (hard disk drive) or an SSD (solid state drive) as the storage device. The storage system is accessed from one or more host devices (for example, host computers) through a network such as a SAN (storage area network) or LAN (local area network). In general, the storage device improves reliability with the use of a high reliability method complying with a RAID (redundant array of independent (or inexpensive) disks) technique.
U. S. Patent Application Publication No. 2009/0144496 discloses an information system capable of compressing data while maintaining a data writing speed from a host computer. According to U. S. Patent Application Publication No. 2009/0144496, the storage device provides a first volume that accepts data write from a host computer and a second volume that compresses and manages data on the first volume. Upon completion of the data write to the first volume from the host computer, the storage device returns a response assuming that a write process to the host computer is completed. Thereafter, the storage device compresses the data asynchronously with the data write from the host computer and stores the compressed data in the second volume.
A publication “Jun Kato, Hiroki Otsuji, Kosuke Suzuki, Mitsuru Sato, Eiji Yoshida: “High-speed writing in in-memory deduplication”, Research report computer system symposium, Nov. 28, 2016, pp. 51-59” discloses a method for achieving both of a response and a throughput by switching a processing opportunity according to an operation rate of a storage device, in a deduplication process for combining duplicate data written from a host computer into one piece.
For example, the “High-speed writing in in-memory deduplication” discloses that “This paper proposes a hybrid method in which characteristics related to an IOPS and a latency depend on different methods, and those methods are selectively used, to thereby realize a low latency of a duty-back method and a high IOPS of a dedup-through method.” In addition, the “High-speed writing in in-memory deduplication” discloses that “This paper proposes a hybrid method in which two methods of a conventional dedup-through method for performing deduplication synchronously and a dedup-back method for performing deduplication asynchronously are compared with each other, a high IOPS performance and a high latency by overhead of a synchronous deduplication process in the dedup-through method, and a low latency and a reduction in IOPS caused by an increase in a tail latency in the dedup-back method are clarified, to thereby aim at performing both of the high IOPS and the low latency by combination of those two methods.”
In other words, according to the “High-speed writing in in-memory deduplication”, when the operation rate of the storage device is low, a response time is shortened by performing the deduplication process after the data write from the host computer is completed, and when the operation rate is high, the deduplication process is performed simultaneously with the data write.